Self-braking shaft positioning means



Oct. 22, 1957 MAYER ET AL 2,810,875

SELF-BRAKING SHAFT POSITIONING MEANS Filed Sept. 15, 1956 1 l I l I l l l l 7a 7s 00 TPUT 3,0550 -S/-/AFT fieaurr/azv MEAN:

INVENTOR.

Aaaorr E MA YER Haw/a RD 5. Rows ATTORNEYS Unite States Patent SELF-BRAKING SHAFT POSITIONING MEANS Abbott F. Mayer and Howard B. Rooks, Marion, Iowa, assignors to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Application September 13, 1956, Serial No. 609,573

4 Claims. (Cl. 318-369) This invention relates generally to shaft positioning means and particularly to means for positioning a shaft to any one of a plurality of predetermined positions.

Prior shaft-positioning means have used the seekingswitch principle for aligning an output shaft. For example, Patent No. 2,476,673 to May and Schwieghofer teaches a seeking-switch system.

In the past, in order to obtain precision in positioning the output shaft of such a system, it has been necessary to provide a mechanical detent or a pawl and stop-wheel mechanism with a clutch to lock the shaft at a particular position upon de-energization of its driving motor by the seeking-switch. Kinetic energy, due to rotation of the driving motor, was dissipated by clutch slippage, since the shaft was then locked; and clutch slippage permitted the motor to coast to a stop.

The present invention eliminates the requirement for a clutch and stop-wheel mechanism with a seekingswitch system, in order to obtain a high degree of preci sion in shaft positioning.

The invention positions its output shaft by means of electrical braking rather than mechanical stopping means.

Also, the electrical braking means provided by this invention minimizes arcing at contacts used in this invention.

Accordingly, the invention is an improvement in a conventional seeking-switch system which has a rotary seeking-switch and a control switch, with oppositelyconstructed rotors. One switch has a rotor with one contact; while the other switch has a rotor with only a single contact missing. A plurality of wires respectively connect the stator contacts of both switches. A continuously-engaging contact connects the control-switch rotor to a power source; and another continuouslyengaging contact connects the seeking-switch rotor to the driving motor, which has its output shaft connected to the seeking-switch through a speed-reduction transmission.

Any one of a number of output-shaft positions may be obtained by setting the control switch to a representative position. A closed circuit is thereby obtained between the motor and the power source until the motor rotates the seeking-switch rotor to a position that finds an open circuit, which is the sought-after position determined by the setting of the control switch.

The invention requires a pair of additional switches. One is a grounding-switch positioned by the controlswitch rotor. The stator of the grounding-switch has the same type of contacts as the control switch; and they are respectively connected together.

The rotor of the grounding-switch has a single nonshorting type of contact, which is capable of engaging only one of its stator contacts at any one time. This switch also has a sliding contact which continuously engages its rotor and is connected to ground. The rotors of the combined switches are connected so that the wire, which is open-circuited at the chosen control ice 2 switch position, is connected to ground by the position of the grounding switch.

The invention also requires another switch, which is positioned by the seeking-switch. It is called herein a speed-reducing switch. The seeking-switch, itself, has a non-shorting type of contact. The added speed-reducing switch also has a single contact, but it is of the shorting type. That is, its rotor has a contact that is capable of engaging two adjacent stator contacts at one time.

The stator contacts of the braking-switch are connected respectively through resistors to the contacts of the seeking-switch.

The speed-reducing switch also has a continuous connection between its rotor and the drive motor. The seeking-switch and speed-reducing switch rotors are coupled to the output shaft of the system through a speedreduction transmission.

Further objects, features, and advantages of this invention will be apparent to a person skilled in the art upon further study of this specification and drawing, in which:

The single figure illustrates a preferred form of the invention.

Now referring to the invention in more detail, the system in the figure shows a control station 1%) and a controlled station 11, which are connected by a plurality of wires 13, 14, 15, and 16. Actually, the invention may use any number of control wires, and each wire provides a separate position for the output shaft. Thus, the four control wires in the figure are for illustrative purposes only.

A rotary-type control switch 20 is provided which has four stator contacts 21, 22, 23, and 24 with a rotor 26 having a conducting periphery except for a notch 27. Rotor 26 engages all of the stator contacts except the one which aligns with notch 27.

A sliding contact 28 continuously engages rotor 26, and it is connected to a power source 29 which may provide either alternating or direct current.

A grounding switch 30 is also provided at control station 10; and it has the same number of stator contacts as control switch 20. The contacts are 31, 32, 33, and 34. Grounding switch 30 has a rotor 36 with a single non-shorting contact 37, which is capable of engaging only one of its stator contacts at any one time. Also, a sliding contact 38, which is grounded, continuously engages rotor 36.

A control knob 40 is connected mechanically to both rotors 26 and 36. A dial 41 cooperates with control knob 40 to indicate the selectable positions of the output shaft. In this example, the positions are numbered t through 4.

Stator contacts 31 through 34 of grounding switch 3% are respectively connected to the stator contacts 21 through 24 of control switch 20.

Rotary-tap switches are generally preferred in the construction of this invention. Such tap switches are usually made in wafer form wherein a single wafer has two rotors with two sets of stator contacts. Accordingly, control switch 20 and grounding switch 30 can be easily made from a single wafer switch which has respective stator contacts connected together.

Controlled station 11 has a seeking-switch 55} and a speed-reducing switch 60. They may also be constructed from a single wafer switch which has separated stator contacts.

Seeking-switch 50 has four stator contacts 51, 52, 53, and 54; and speed-reducing switch 60 has four stator contacts 61, 62, 63, and 64. Stator contacts 51 through 54 are connected respectively to stator contacts 61 through 64 through resistors 71, 72, 73, and 74, which are equal in resistance value.

The rotor 56 of seeking-switch 50 has a single nonshorting type of contact 57. On the other hand, the rotor 66 of speed-reducing switch 60 has a single shorting type of contact 67.

A sliding contact 58 continuously engages the rotor of seeking-switch 50; and another sliding contact .68 continuously connects to the rotor of braking-switch 60.

A driving motor 76 has one side connected to ground, and has its other side connected to sliding contacts 58 and 68.

A speed-reduction means 77, which is generally a gear transmission, has its input connected to the output shaft 78 of driving motor 76; and the output 79 of reduction means 77 is connected to rotors 56 and 66 to provide the output shaft of the system.

The connecting wires 13 through 16 respectively connect the stator contacts of seeking-switch 50 to the stator contacts of control switch 20.

In operation, control knob 40 is set to any of its discrete positions, which corresponds to a required indicated position on dial 41 for output shaft 79.

As an example of operation of the invention, let the assumed that it is required to change the output-shaft position from that illustrated to positionfour.

The illustrated situation is a steady state condition for the system, in which motor 76 is disconnected from power source 29 by virtue of the positions of the respective rotors in the system.

When control knob 40 is moved to position four, control-switch notch 27 will align with stator contact 24, and formerly open-circuited stator contact 23 will now engage rotor '26 to provide a connection from power source 29 to lead 16 to initially connect motor 76 to power Source 29 through seeking-switch rotor projection 57. Thus, motor 76 will be energized and will begin rotating seeking-switch rotor 56 and speed-reducing switch rotor 66 through gear reduction 77 in the direction illustrated by arrows.

After these rotors have rotated approximately 25 degrees from the illustrated position, seeking-switch projection'57 will disengage from stator contact 53 and will not be engaged with any of the stator contacts, since it is a non-shorting type of contact.

However, at this instant speed-reducing switch rotor projection 67 will still engage stator contact 63 to maintain a connection between motor 76 and energized lead 16. However, resistor 73 is between lead 16 and speedreducing switch 64 while on the other hand, there were no resistors in the motors current path whena connection was obtained through seeking-switch 56. .Accordingly, motor 76 operated at full speed while seekingswitch 50 provided a connection. However, after disconnection of the seeking-switch, the remaining connection to the motor is only through speed-reducing switch 66, which provides a reduced voltage to motor 76, due to the voltage drop across resistor 73. vThus, the motor rotates at a slower rate. of speed, and the rotational speed of output shaft 79 is reduced to a low value, which is, for example, one-half its previous speed.

After further rotation of output shaft 79 and before seeking-switch rotor projection 57-.engages stator contact 54, shorting projection 67 of speed-reducing switch-'60 will simultaneously engage stator contacts 63 and 64. However, contact 64 is connected to grounded contact 34 by means of resistor 74; and resistor 74 is connected across motor 76 to reduceits speed further if the resistors have low resistance values.

Shortly thereafter, the trailing edge of braking-switch projection 67 will disengage from contact 63. This will disconnect power source 29from motor '76; but since no braking is applied, motor 76 will continue; to rotate under its momentum.

Very soon, seeking-switch projection .57 will engage .stator contact-54 andi-then braking is. applied to quickly bring output shaft 79 to a halt. This occursbecause as 54, both sides of motor 76 become grounded; and a large surge of current is caused through motor 76 by its back E. M. F. which quickly stops it. Although the motor may coast many degrees, output shaft 79 will coast very little due to gear reduction means 77; and shaft 79 may coast less than one degree. Thus, the accuracy of the system is generally improved by increasing the ratio of reduction means 77. m

If the trailing edge of projection rotor 67 has not completely cleared its stator contact when seeking-switch rotor projection 57 becomes grounded, no large difficulties are encountered. In such case, a circuit is provided through resistors 74 and 73 to the power source, which will only cause energy dissipation that in some cases may be undesirable. This can easily be avoided by proper alignment between rotors 56 and 66.'

Arcing will occur at the instant that the trailing edge of braking-switch projection 67 leaves contact 63, because the circuit is completely broken at that time. However,

at that instant, motor 76 willbe operating at a greatly reduced speed. Accordingly, verylittle arcing will ,occur. Nevertheless, any burning of the trailing edge of projection 67 will not affect the accuracy of the system, since thatis determined by the position of the leading edge of projection 57.

Any number of shaft positions may be provided in the system. The addition of another control wire and stator contact to each switch will be requiredfor each added position. Accordingly, the sector of are required by the rotor projections will become smaller as the number of shaft positions is increased. However, the diameter of the rotormay be increased.

It is therefore realized that the invention provides a shaft positioning system which has automatic dynamic braking to position its output shaft at any one of a plurality of discrete output-shaft positions.

Although this invention has been describedwith respect to a particular embodiment, it is not to'be so limited as changes and modifications may be made therein which are within the full and intended scope of the invention as defined by the appended claims.

I claim: 1. Dynamic braking means for a seeking switch system having a control switch and a seeking-switch connectedby a plurality of wires, comprising a grounding switch having'its rotor connected to the rotor of said control switch, said grounding switch rotor having a single non-shorting contact, with the stator contacts of said grounding switch being respectively connected to the stator contacts of said control switch, a speed-reducing switch having its rotor coupled to said seeking-switch rotor, said speed-reducing switch rotor having a single short-type contact, aplurality of resistors connected re spectively betweenthe stator contacts of said speed-reducing switch and said seeking-switch, a motor being continuously connected in series with the rotors of said seeking-switch and said speed-reducing switch, and gearreduction means having its input coupled to theoutput shaftof said motor and having its reduced output convnectcd to the rotors of said speed-reducing switch and said seeking switch.

2. Electrically-braked shaft-positioning means comprising a rotary control-switch, and a rotary seekingswitch, each having it number of stator contacts, with n number of wiresrespectively connecting the contacts of said control switch to the contacts of said seeking-switch, said seeking-switch rotor having a single non-shorting contact, and said control-switch rotor formed with an insulated notch, a rotary grounding-switch having a single rotor contact, with its rotor being coupled to said control-switch rotor, and having n number of stator contacts respectively connected to the stator contactsof said control switch, a speed-reducing switch having a rotor with a-single shorting-type contact, .and 11 number of stator contacts, a plurality of resistors connected respectively between said speed-reducing switch stator contacts and said seeking-switch stator contacts, each of said rotary switches having a sliding contact that continuously engages its respective rotor, with the sliding contact of said grounding-switch connected to ground, and with the sliding contact of said control-switch connected to the power source, a motor having its armature connected serially between ground and the connected sliding contacts of said speed-reducing switch and said seekingswitch, gear-reduction means having its input coupled to the shaft of said motor and having its speed-reduced output coupled to the rotors of said seeking-switch and said speed-reducing switch.

3. Dynamic-braking means for a seeking-switch system comprising a seeking-switch having a rotor with a single non-shorting type of contact and n number of stator contacts, a control switch having a notched rotor and n number of contacts, n number of control wires respectively connecting the stator contacts of said seekingswitch and control switch, a grounding switch having n number of stator contacts, and a rotor with a single non-shorting contact coupled to the rotor of said control switch, said grounding switch having a grounded contact continuously engaging said rotor, with the stator contacts of said grounding switch being respectively connected to the stator contacts of said control switch, a speed-reducing switch also having n number of stator contacts and a rotor having a single shorting-type of contact, a plurality of resistors, with said resistors being respectively connected between stator contacts of said seeking-switch and said speed-reducing switch, a pair of sliding contacts continuously engaging the rotors of said speed-reducing switch and said seeking-switch, a driving motor for said seeking-switch system having one side connected to ground and the other side connected to the sliding contacts of said speed-reducing switch and said seeking-switch, and speed-reducing means coupling the shaft of said motor to the rotors of said seeking-switch and said speed-reducing switch.

4. Dynamic braking means for a shaft-positioning system having a seeking-switch with a shorting-type rotor, and a control switch with a notched rotor, a plurality of wires respectively connected between the stator contacts of said control switch and the stator contacts of said seeking-switch, each of said switches having a respective sliding contact engaging its rotor, with a power source connected to the sliding contact of said control switch, and a motor connected serially between ground and the sliding contact of said seeking-switch, gearreduction means connected between the output shaft of said motor and the seeking-switch rotor, a grounding switch, a control knob coupled to the rotors of said grounding switch and said control switch, said grounding switch rotor having a non-shorting single projecting contact on its rotor and a sliding contact connected to ground, with the stator contacts of said grounding switch being connected respectively to the stator contacts of said control switch, a speed-reducing switch having its rotor fixed with the rotor of said seeking-switch, said speed-reducing switch rotor having a single shortingtype projecting contact, with a sliding contact that continuously engages said speed-reducing switch rotor connected to the sliding contact of said seeking-switch, and a plurality of resistors respectively connected between stator contacts of said speed-reducing switch and the stator contacts of said seeking-switch, and said resistors each having a resistance value of the same order as the dynamic resistance of said motor.

No references cited. 

